Multimode lidar receiver for coherent distance and velocity measurements

Abstract

The subject matter of this specification can be implemented in, among other things, systems and methods that enable lidar devices capable of detecting and processing multiple optical modes present in a beam reflected from a target object. Different received optical modes can be spatially separated and electronic signals can be generated that are representative of a coherence information contained in various optical modes. Multiple generated electronic signals can be amplified, phase-shifted, mixed, etc., to identify signals, individually or in a combination, that can be used for identification of a range and velocity of the target object with the highest accuracy.

What is claimed is: 
     
         1 . A system comprising:
 an optical subsystem configured to:
 receive a beam reflected from an object, the beam comprising a plurality of modes; 
   a plurality of light detectors to generate a plurality of electronic signals, each light detector of the plurality of light detectors configured to generate a respective electronic signal of the plurality of electronic signals, the respective electronic signal representative of a difference between a respective mode of the plurality of modes and a local oscillator LO copy of a beam transmitted towards the object; and   one or more circuits configured to:
 adjust at least one of a phase or amplitude of a subset of one or more electronic signals of the plurality of electronic signals; and 
 determine, based on at least the subset of the one or more electronic signals, one or more characteristics of the object, wherein the one or more characteristics comprise one or more of:
 a velocity of the object, or 
 a distance to the object. 
 
   
     
     
         2 . The system of  claim 1 , further comprising an RF circuit configured to impart an angle modulation to the beam transmitted towards the object, wherein the angle modulation comprises at least one of a phase modulation or a frequency modulation. 
     
     
         3 . The system of  claim 1 , wherein the optical subsystem is further configured to:
 deliver each of the plurality of modes to a respective light detector of the plurality of light detectors.   
     
     
         4 . The system of  claim 1 , wherein the optical subsystem is further configured to:
 use a diffractive optical element to spatially separate the plurality of modes.   
     
     
         5 . The system of  claim 4 , wherein the diffractive optical element comprises a holographic optical element. 
     
     
         6 . The system of  claim 1 , wherein the difference between the respective mode and the LO copy comprises a phase difference between the respective mode and the LO copy. 
     
     
         7 . The system of  claim 1 , wherein the one or more circuits comprise:
 a combiner to produce a combined electronic signal based at least on the subset of the one or more electronic signals, wherein the one or more characteristics of the object are determined based on the combined electronic signal.   
     
     
         8 . The system of  claim 1 , wherein the subset of the one or more electronic signals is characterized by highest signal-to-noise (SNR) ratios of the plurality of electronic signals. 
     
     
         9 . The system of  claim 1 , wherein the optical subsystem comprises a photonic integrated circuit (PIC) having an array of waveguides to deliver each of the plurality of modes to a respective light detector of the plurality of light detectors. 
     
     
         10 . A sensing system comprising:
 an optical subsystem to:
 receive a beam generated upon interaction of a sensing beam with an object, wherein the received beam comprises a plurality of optical modes; 
   a light detection subsystem, operatively coupled with the optical subsystem, to:
 generate a plurality of electronic signals, wherein each of the plurality of electronic signals is obtained using a respective one of the plurality of optical modes; and 
   one or more circuits, operatively coupled with the light detection subsystem, to:
 process the plurality of electronic signals to obtain a combined electronic signal, and 
 determine, using the combined electronic signal, one or more characteristics of the object, wherein the one or more characteristics of the object comprises at least one of a velocity of the object or a distance to the object. 
   
     
     
         11 . The sensing system of  claim 10 , wherein each of the plurality of electronic signals is further obtained using a local copy of the sensing beam and is representative of a phase difference between a respective one of the plurality of optical modes and the local copy of the sensing beam. 
     
     
         12 . The sensing system of  claim 10 , wherein to obtain the combined electronic signal, the one or more circuits are to:
 identify one or more electronic signals of the plurality of electronic signals characterized by highest signal-to-noise (SNR) ratios; and   combine the one or more identified of electronic signals to obtain the combined electronic signal.   
     
     
         13 . The sensing system of  claim 10 , wherein to obtain the combined electronic signal, the one or more circuits are to:
 adjust one or more properties of at least a first electronic signal of the plurality of electronic signals, wherein the one or more properties comprise at least one of an amplitude or a phase of the first electronic signal.   
     
     
         14 . The sensing system of  claim 13 , wherein the one or more properties of the first electronic signal are adjusted to improve a signal-to-noise (SNR) ratio of the combined electronic signal. 
     
     
         15 . A method comprising:
 receiving a beam reflected from an object, the beam comprising a plurality of modes;   generating a plurality of electronic signals, wherein each electronic signal of the plurality of electronic signals is representative of a difference between a respective mode of a plurality of modes of the reflected beam and a local oscillator (LO) copy of a beam transmitted towards the object;   adjusting at least one of a phase or amplitude of a subset of the one or more electronic signals; and   determining, based on at least the subset of the plurality of electronic signals, one or more characteristics of the object, wherein the one or more characteristics comprise one or more of:
 a velocity of the object, or 
 a distance to the object. 
   
     
     
         16 . The method of  claim 15 , wherein generating the plurality of electronic signals comprises:
 delivering each of the plurality of modes to a respective light detector of a plurality of light detectors.   
     
     
         17 . The method of  claim 16 , wherein delivering each of the plurality of modes to the respective light detector comprises:
 using a diffractive optical element to spatially separate the plurality of modes.   
     
     
         18 . The method of  claim 16 , wherein the plurality of modes is delivered to the plurality of light detectors using an array of waveguides of a photonic integrated circuit (PIC). 
     
     
         19 . The method of  claim 16 , wherein determining the one or more characteristics of the object comprises:
 combining at least the subset of the plurality of electronic signals to produce a combined electronic signal; and   determining the one or more characteristics of the object based on the combined electronic signal.   
     
     
         20 . The method of  claim 19 , wherein the subset of the plurality of electronic signals is characterized by highest signal-to-noise (SNR) ratios of the plurality of electronic signals.